Introduction: How to Make a Spot Welder - for Cheap!!

Picture of How to Make a Spot Welder - for Cheap!!

Step 1: You Might Be Surprised How Cheap It Can Be

Picture of You Might Be Surprised How Cheap It Can Be

Have you seen the video above?  If not, take a look now because it will help you as you go along in this instructable. 

A typical resistance Spot-Welder can range in price from about $200-$800, but with a little resourcefulness, and a bit of free time, you can make one like this for about $10 or less.

Spot welders are used to fuse thin sheets of metal together.  They are most likely used in the auto industry, as well as HVAC for welding metal ducting.  

There are a couple of videos you should see before starting on this project, because you may want some background on how the device works.

Here is how to: Make The Metal Melter

Here is what it can do:  The Metal Melter

Step 2: Take Some Measurements

Picture of Take Some Measurements

Measuring the base of my Metal Melter, I found it was about 4-1/4".

I found a 6' length of 1x6 common board for about $4, which actually measures out at 5-1/2", so it will work just fine.

Two pieces of the board will need to be cut to 12" lengths (5-1/2" x 12"), but the rest can be pushed through a table saw to trim the width down to 4-1/2" (1/4" wider than the transformer base).

Step 3: Roughing the Case Together

Picture of Roughing the Case Together

The piece of common board that you just trimmed down to 4-1/2" wide can be cut into 3 pieces measuring;

  4"  x  4-1/2"
12"  x  4-1/2"
24"  x  4-1/2"

The other 2 pieces of the common board should measure;

12" x 5-1/2" (x 2 pieces)

You'll also need 4 pieces of 2x2 measuring;

2" x 2" x 13-1/2" (x 2 pieces)

2" x 2" x 4" (x 2 pieces)

This is all the wood you'll need for building the casing.

I used a 3/4" rounding bit and my router to smooth the edges and give it a cleaner look.  

This is roughly how it will look when it's assembled.

Step 4: Prepping the Pieces

Picture of Prepping the Pieces

A notch needs to be cut on one of the 2x2 arms, and you'll see what this is for later on.  I found a piece of scrap can be used as a template. 

The notch can be cut out with a bandsaw, wood saw, or any other saw you can get creative with.  I used a jig-saw, but wouldn't recommend it as the safest option.

The back panel (4" x 4-1/2") also gets holes cut that will accommodate an electrical light switch, and a notch for a power cable.

The pieces get sanded, primed, and painted.  I chose to paint this black and yellow. 

Step 5: Additional Materials

Picture of Additional Materials

When I salvaged the Microwave Oven Transformer in this previous project , I saved some of the other components that can be used for our Spot Welder;

- The power cord
- The door handle
- Wires for the transformer terminals, with insulated spade connectors
- Power switch, with wires and insulated spade connectors

Aside from these, the only other items you'll need are;

- Simple light switch, with faceplate
- Copper offset terminal lugs that will hold  ( x 2)
- 1/4" hex screws( x 2)
- Small nails ( x 2)
- Length of solid copper wire (4AWG is better, but I used 6AWG in this project)

The solid copper wire can be snipped into 1" lengths, that fit nicely into the terminal lugs.  

The lugs have a mechanism that can be tightened with a screwdriver to secure the connection with the wire.  The tighter the better.

Step 6: Start Assembly

Picture of Start Assembly

Now that the wood is painted, finished, and dry (I gave it about 2 days), the unit can be assembled.

The back panel is for a light switch and a power cord.  

Before screwing the panel into the base, make sure your cord goes in first.  The thick piece at the end of the cord prevents it from pulling back though the hole.  

This is also the time to add the 2 pieces of 2" x 2" x 4" support blocks to the base.  Be sure of your measurements before you screw them down.  You want them to end up flush with the side panels when it's done.

The Metal Melter can be placed inside now, and when a good position is found, can be screwed to the base with a couple of small screws.

Now it's time to wire up the electrical system.

Step 7: The Electrical System

Picture of The Electrical System

Starting with the power cord coming into the casing, I stripped the black wire, and attached it to the bottom terminal of the light switch.

Next, I attached one of the wires I had salvaged, to the right terminal on the transformer, stripped the other end, and attached that to the top of the light switch.

The electrical could almost be finished here, but I wanted to add another switch, for safety and convenience, and that's where the salvaged switch from the microwave hack comes in.

The two wires attached to the switch can be wrapped with electrical tape to secure the connection and help insulate from electric shock.  

The both ends of the wires are stripped so the copper wire is exposed.

One wire connects to the left terminal of the Metal Melter's primary coil, and the other wire connects to the white wire on the power cable that runs back to the house.  

The electrical system is complete!

Step 8: Close It Up and Add the Arms

Picture of Close It Up and Add the Arms

The sides can be screwed on with 6 wood screws on each side.  I used 2" wood screws after drilling pilot holes to make sure the wood didn't split.

The trigger switch is attached near the tip of the top welder arm, and at a bit of an angle so it can be pressed easily.  I found that 2 small nails held this in place perfectly.  

Both arms can get inserted into the front of the casing, and with a bit of guesswork, a hole can be drilled through the side of the casing and into the end of the arms, so that when a nail is inserted, it will pivot.  

Now you can see why we needed the notch in the arm.

To help the arm stay in an upright position, I added a couple of screws and rubber bands to keep the tension.

This also provides a little back pressure, and stabilization when using the welder.  

Step 9: Adding the Electrodes

Picture of Adding the Electrodes

The copper lugs can be added to the tips of the arms.  

I drilled pilot holes with a 3/16th drill bit, then secured the lugs by pushing the hex bolts first through the hole in the lugs, then through the lugs on the the Metal Melter terminals.

One in the top, and one in the bottom.  It shouldn't matter which way they go, but I chose to make my top cable on the same side as the switch because it was easier to handle.

If the electrode tips don't line up perfectly, it's easy to bend them a little until they do.  

When finished, it should look like this.

Step 10: The Finished Result

Picture of The Finished Result

The Spot Welder is finished!

It will only work if the safety switch on the back is turned on, and even then, no power is delivered until the thumb operated switch is pressed.

To use, place thin sheets of metal between the electrode tips, then press the button with your thumb for about 3-4 seconds.

The massive electrical current pushing through the metal, heats it up to the point where it fuses with the other sheet.  

You can release your thumb from the switch and wait until the weld cools enough to handle.

Welding these metal washers worked so well, I couldn't break them by hand.  I had to use 2 pairs of pliers to get them to snap.  

When the energized electrode tips touch each-other, you can see the high-amp sparks.

Note: Burning galvanized metals may release zinc-oxide fumes.  Welding should be done in a well ventilated area.

Step 11: Additional Features

Picture of Additional Features

The electrode arms are only held in with nails, so if the nails are removed, the arms can be removed to extend the welders reach, and access difficult angles.

They go back together very easily, and the elastic can be conveniently replaced when necessary.

When the electrode tips are spent, it's easy to unscrew the bolt holding them in place, and add a fresh piece of copper wire.

Copper wire is relatively cheap.  You can get a pice of 12" 4AWG wire for about a dollar.  That means each tip is less than 10¢ each!

The power of the metal melter is still evident in the way this can bring iron metal to a boil!  Be careful running the welder too long because there is a chance the wires will get so hot that the insulation on the cables will start smoking and melt.

Now you know how to make my version of a cheap Spot Welder.  

If you haven't seen the step-by-step video, you can still see it here.

If you like this project, perhaps you'll like some of my others.  Check them out at


clickbang44 (author)2017-06-22

Thank you for sharing this build. I had someone throw out a microwave before you made this and I dissassembled it and was waiting for a use to the transformer - now I have it! I will post pics when I get done and already have a need for a spot welder to finish another projest - TIMING - YEAH!!!

Sythe101 (author)2016-09-23

Hello. I've tried making this spot welder/ metal melter but i have run into a problem I don't think my breaker likes it very much. I have a transformer with about 100 wraps and used 2 gauge wire and wrapped it two times. I tried to melt some metal but my breaker cut it off. Im wondering if i can use some higher gauge wire with more windings to up the amperage slower. Any tips or suggestions?

Yonatan24 (author)2016-08-11

Hi, I've added your project to "The Ultimate Collection of DIY Workshop Tools" Collection

Here is the link If you are interested:

Scout. made it! (author)2016-07-30

Thanks for the great instructable! Still a little bit of a work in progress, but it works! I think it would be cool to add lights to the enclosure. I painted it with trunk liner and a high temperature engine paint. Thanks again!

twotimefranks (author)2016-05-06

Quick safety question. I have rewrapped the secondary of my mot with 2/0 with only a couple turns so I'm getting 2.5 v out. So at 12 amps in at 120 I have the potential of 575 amps out. So I'm just a tab bit nervous about holding the thing I want to spot weld....Even though I realize at 2.5 v it'd have a pretty hard time of poking me. You guys have had no problems?

taloskriti made it! (author)2016-04-03

Here's my version inspired by your instructable. Mine is not as polished as yours but has an added extra feature. In the build, I included the fan that was inside the microwave to cool the transformer. I added some ventilation holes from the original microwave chassis as well. Also the offset copper lugs where impossible to find locally and impossible to buy online because I only found them in US stores and couldn't afford the cost. So I improvised and made them from scratch! I used a copper pipe for that. As for the electrodes I had much trouble to find sufficiently thick copper wire, so I cut two pieces of a copper plate used in lightning rod installations. I think that they could be replaced by soldering iron tips. Any thoughts about that?

jlouhi (author)2016-01-23

Hey! Is Someone made it to metal frame? Not wood...

shenry7 (author)2016-01-20

Would this weld light aluminium?

erikburrows made it! (author)2015-10-11

I made mine with the effector separate from the transformer, as I intend to refine it to be smaller and more delicate, but this first rev worked just fine, thanks!

Charles51 (author)2014-07-19

I put one of these contraptions together using your video as a guide and those of several others on YouTube. Melts wire amazingly. As an artist I need to spot weld wire together to form armatures. The wire gets red hot and will melt but it does not weld together and comes apart when additional pieces are added. Any idea why?

fredlam (author)Charles512015-09-25

Not all joints will weld, particularly if made from different metals, but most steel, iron, stainless steel will give you no problems.

Possum Living (author)Charles512015-01-13

Sounds like too much resistance in the wire. Have you tried using bigger wire? Also keep the wire run from the transformer as short as possible.

JeffG2 (author)2015-05-16

Thanks for this project. I managed to bodge one together and to my surprise it actually works - a bit TOO well actually. So, I have a couple of questions:

1) I am using 4 AWG THHN wire and it's very stiff. is there any way to connect thinner gauge wire to the thick leads? I want to make some sort of hand piece or probes to get into tighter spots (as opposed to having these fixed in one place and maneuvering the pieces to be welded under it). Leads to my next question…

2) The heat created is too intense and actually melts the metal too quickly (I am creating armatures out of relatively thin garment hanger wire). Is there any way to attach a dimmer switch/potentiometer to this? And if so, will a regular household dimmer switch work or do I need something else?

Any answers and suggestions are greatly appreciated.

fredlam (author)JeffG22015-09-25

Very heavy currents require thick wire. Thinner wire would overheat and burn.

To control the heat imparted onto the workpiece, just use shorter power intervals. I find most of the time one or two seconds will do the trick on most materials.

fredlam made it! (author)2015-09-25

This is my contraption, using materials in hand including old drawer fronts and a piece of rectangular mild steel tube from an old shelf. The winding is 3 turns of #2 wire from a scrapyard bought for a penny. The tongs are 3/8" instead of 1/4" tapered down on a drill press and file. Took me only half a day of work. Results are astounding, although I had to practise a little on different material and different thickness to get the best results.

Yonatan24 (author)2015-09-25

I wish I could make one... Maybe in a couple years!

Pondguy made it! (author)2015-08-28

This was a fun project. I was surprised at how well it worked. it has come in handy on a few projects.

kweixelman made it! (author)2015-05-12

I wired in the light and use pallet wood total if 15$ spent.

EvolvedAwesome (author)2015-03-24

Looks awesome

harry.godwin3 (author)2014-11-26

Anyone noticed we're trying to fit 6 inches of 2x2 into a 4.5 inches of space?

isnell (author)harry.godwin32015-02-25

2x2s are 1.5"x1.5"

vshljn05944 (author)2015-02-10

Sir can you please tell the rating of transformer you used in this project

that is the input and output voltage rating and current required to generate the melting at the desired spot to melt

pandamopeds13 (author)2015-01-15

Whatisthe thickest metal this will tolerate? Again, another fantastic write up sir.

Possum Living (author)2015-01-13

Great instructable, Grant!

RobertP7 (author)2015-01-07

Hi, enjoy seeing what you have made. On the spot welder what wire are you using leading to the welding tips? 2/0 seems too stiff to have the arms removable or did I just miss something here?


Lots of projects I see I'm going to start doing in my retirement years!

fredF1 (author)2014-11-21

Are the transformer shunts left in or taken out?

harry.godwin3 (author)fredF12014-11-27

The shunts are removed.

pnosko (author)2014-11-15

Let me ask a dumb question. You are using 1/4" hex screws to mount the terminal lugs to the arms. Considering that your metal melter videos show you melting similar screws, what is preventing these mounting screws from melting?

pnosko (author)pnosko2014-11-16

Answering my own question below after watching some educational electricity videos, I think the reason the 1/4" bolts are not affected is because the leads direct contact to the terminals make that the shortest path for the current, so it does not actually pass through the bolts.

Fission Chips (author)2014-10-23

Cool! I know this is dangerous to some extent, but exactly how dangerous is it?

felippec1 made it! (author)2014-09-03

I made it and work fine. thank you for inspiration.

Felippe Cardelino


SIRJAMES09 (author)2014-08-15

Sir, you never cease to amze me!

this is just too cool!!! :)

TY for sharing Sir.

stamatelos (author)2014-03-21

Thank you it is very usuful i will try to bild sun

I_StarkGuy made it! (author)2014-02-26

Finished mine! I changed the design to adapt it to available materials and I added the microwave fan to cool the MOT.

Can you weld galvanized steel? Mine is not able to do it, though my math gives me above 950 amps.

JestGold (author)I_StarkGuy2014-02-28

I think you can weld galvanized BUT the fumes given off are very toxic and potentially lethal. If you have to do this use a respirator, work outside or better yet, just try to avoid this if at all possible.

I_StarkGuy (author)JestGold2014-02-28

It is not that toxic in small quantities. And I work outside and I have been exposed to the fumes when melting screws.

JestGold (author)I_StarkGuy2014-02-28

The toxicity of galvanized metal when welded was one of the first lessons taught me by a pro. That said, just be careful (really, wear a respirator no matter where you are)!

JestGold (author)2014-02-28

Really like these projects and the metal melter/spot welder appear to be exactly what I need. Was wondering a couple of things:

a) I create metal sculptures from thin gauge wire rod and is there any way to regulate the amount of power so the metal fuses instead of melting (the spot welder seems to do just that)? and…

b) can the arms be separated or made into some sort of hand piece to make it more practical/accessible to the work?

Many thanks!

reddrexx (author)2014-01-04

I made one! But changed up the arms a bit. It works great.

quantumquark (author)2013-12-28

Are you sure you don't have AWG 2/0 wire ? It looks thicker than my AWG 2 wire. (2/0 is really 00 awg)

ccrow2 (author)2013-10-10

I have transformer from a die hard 6 and 12 volt battery charger I'm wondering how that would work, several input leads on the primary, the charger also had a 75 amp jump start setting also. Hmmm anybody wanna help me with where to start 6v 12v? I'd better do some math.

Pecheck (author)2013-09-12

late reply, but very awesome project. I'm definitely building one. I'll just ad a computer fan and some vent holes to by transformer housing.

kade199 (author)2013-07-26

hey i was just wonder if for the MOT i should use the 2 AWG (since the 4 AWG melted) or if i should do the 8 gauge wire wrapped 16 times like in your arc welder video? which would be better overall for the spot welder?

mattbeowulf (author)kade1992013-07-29

I would think that if 8AWG wire wrapped 16 times worked better for the spot welder, then he probably would have said so, since they are both HIS videos ;-) But maybe he learned since making this one, and hasn't updated...
At any rate, 16 turns on the same core would result in higher voltage -- haven't watched the arc welder video yet -- guessing about 20V. Along with V increase, I (current, and resulting heat) goes down. I bet that the 2AWG (same number of turns) is the way to go here, since heating will occur in the secondary AND the work. I think the idea is to get the high current for the heat, and just make sure not to try melting anything that melts easier than the secondary's insulation! Assuming insulation was no issue, you'd simply have to keep the work easier to melt than the secondary itself, which is probably a complex relationship between relative masses and melting points.

But now I'm gonna have to go watch the arc welder video... are those capacitors I smell? :-)

GraphixS6 (author)2013-06-01

Do you know any place that you can reliably get dead microwaves. It seems my neighbors don't have a habit of just throwing them out.

f.masoni (author)2013-04-09

I love this project, i want to make one of my own but have a couple of questions.

Where i live the voltage of a power outlet is 220v does this change anything?

Also is it possible to make one that welds two separate spots at once with the same transformer.

Best Regards

calebwang (author)2013-03-09

I love your project. Your video editing is top notch as well.

Thank you! Thank you!

th3_jungle_inv3ntor (author)2013-03-09

Hi there. Thanks for this amazing project! I was amazed how easy it was to make. Luckily when I discovered this project, I knew were an old microwave was. I live in a small village in Guyana and most people here don't have microwaves. It was from a small restaurant. I successfully got the transformer out which was a little scary even for a 16 year old. I built a deluxe version of your design with the microwave light and fan incorporated in, along with four switches. My problem was that I didn't have any solid copper rod to use for the contacts. I had a few bronze welding rods so I used a small piece of that, instead. My welder is putting out about 1v. It melts nails and about anything else. I have not gotten it to actually weld. The metal to weld gets red hot but doesn't weld together. Any idea's whats wrong? I would appreciate any help. It's fun to melt metal, but it doesn't weld. Thanks.

Thanks for your comment! I'd love to see a little video of your welder as a video response to my video on YouTube, if you get a chance to do that?

It may help to press the contacts together harder when welding. You may also need more power. (Eg. Bigger transformer)

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Bio: Random Weekend Projects
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